it isn't like they got some purple gunk they put on there. no, no, no. it's very, very clear. but the thickness is such that it will cancel out the yellow and give you the complementary color, so you see your coded lenses, the nice purplish color. ain't that neat? you like? yeah. yeah. i bet-- gang, we'll talk about polarization. we talked about charged polarization before. we talked about, like, negative, being on one side of a molecule, positive, on another. polarization, in this sense, is altogether different. we're talking about the lineup of waves. if i take a rope and tie it to the wall, and i shake the rope up and down like this, guess which way the wave will vibrate. how many say, "oh, probably like this"? hey, come on, come on. trick question. no, no. if i shake it up and down like that, the rope will vibrate like that. and the vibration is aligned. we don't say aligned. we say it's polarized. if i shake the rope back and forth horizontally, then i'll generate a horizontally polarized wave. okay? you saw the example in the textbook.